Receptors for many cardiac hormones and neurotransmitters are coupled to their effector enzymes or ion channels by a family of heterotrimeric GTP- binding proteins (G proteins) made up of alpha and betagamma subunits. These proteins act as critical control points for directing signals initiated at the cell surface to specific intracellular second messenger pathways. They are essential for normal cardiac function, and their derangement in pathological states including heart failure may contribute to abnormal responses of the heart to some agonists. Because the G proteins are structurally similar proteins whose functions sometimes overlap, it has been difficult to sort out the role of particular G proteins in complex cellular responses. Such a dissection of the signalling system is necessary before it would be possible to realize their potential usefulness as targets for pharmacological intervention in clinical states such as heart failure. The long-term goal of these studies is to define the role of individual G proteins in the normal and pathological function of cardiac cells. We propose to use genetic tools to create model systems in which we can study the biochemistry, cell biology and whole animal physiology of hearts with specific and reproducible alterations of signalling pathways. The strategy is to create transgenic models that express mutated alpha subunits only in the myocardium. These mutations will either cause the alpha subunits to be constitutively active or to act in a dominant negative fashion to inhibit the function of endogenous subunits. An alternative strategy will be to block G protein synthesis expressing antisense mRNA in the myocardium. These animals will provide a source of hearts all carrying the same modification that can be used to study the biochemistry of signal transduction, for analysis of the function of dissociated cultured cardiocytes, and for evaluation of the function of the whole organ both ex vivo and in vivo in the basal state and after induction of hypertrophy. These transgenic animals will make it possible eventually to define the contribution of particular G proteins to cardiac responses to those stresses that lead initially to hypertrophy and finally to failure.